The present invention relates generally to inkjet printing mechanisms, and more particularly to a single-pass wiper system that removes ink residue from an inkjet printhead in a more time efficient manner than earlier systems, allowing the printhead to more quickly return to printing which increases the throughput rating of the unit (measured in pages per minute).
Inkjet printing mechanisms use cartridges, often called xe2x80x9cpens,xe2x80x9d which eject drops of liquid colorant, referred to generally herein as xe2x80x9cink,xe2x80x9d onto a page. Each pen has a printhead formed with very small nozzles through which the ink drops are fired. To print an image, the printhead is propelled back and forth across the page, ejecting drops of ink in a desired pattern as it moves. The particular ink ejection mechanism within the printhead may take on a variety of different forms known to those skilled in the art, such as those using piezo-electric or thermal printhead technology. For instance, two earlier thermal ink ejection mechanisms are shown in U.S. Pat. Nos. 5,278,584 and 4,683,481. In a thermal system, barrier layer containing ink channels and vaporization chambers is located between a nozzle orifice plate and a substrate layer. This substrate layer typically contains linear arrays of heater elements, such as resistors, which are energized to heat ink within the vaporization chambers. Upon heating, an ink droplet is ejected from a nozzle associated with the energized resistor. By selectively energizing the resistors as the printhead moves across the page, the ink is expelled in a pattern on the print media to form a desired image (e.g., picture, chart or text).
To clean and protect the printhead, typically a xe2x80x9cservice stationxe2x80x9d mechanism is supported by the printer chassis so the printhead can be moved over the station for maintenance. For storage, or during non-printing periods, the service stations usually include a capping system which substantially seals the printhead nozzles from contaminants and drying. Some caps are also designed to facilitate priming, such as by being connected to a pumping unit that draws a vacuum on the printhead. During operation, clogs in the printhead are periodically cleared by firing a number of drops of ink through each of the nozzles in a process known as xe2x80x9cspitting,xe2x80x9d with the waste ink being collected in a xe2x80x9cspittoonxe2x80x9d reservoir portion of the service station. After spitting, uncapping, or occasionally during printing, most service stations have an elastomeric wiper that wipes the printhead surface to remove ink residue, as well as any paper dust or other debris that has collected on the printhead. The wiping action is usually achieved through relative motion of the printhead and wiper, for instance by moving the printhead across the wiper, by moving the wiper across the printhead, or by moving both the printhead and the wiper.
To improve the clarity and contrast of the printed image, recent research has focused on improving the ink itself. To provide quicker, more waterfast printing with darker blacks and more vivid colors, pigment-based inks have been developed. These pigment-based inks have a higher solid content than the earlier dye-based inks, which results in a higher optical density for the new inks. Both types of ink dry quickly, which allows inkjet printing mechanisms to form high quality images on readily available and economical plain paper, as well as on recently developed specialty coated papers, transparencies, fabric and other media. Unfortunately, the combination of small nozzles and quick drying ink leaves the printheads susceptible to clogging, not only from dried ink and minute dust particles or paper fibers, but also from the solids within the new inks themselves. Partially or completely blocked nozzles can lead to either missing or misdirected drops on the print media, either of which degrades the print quality. Thus, keeping the nozzle face plate clean becomes even more important when using pigment based inks, because they tend to accumulate more debris than the earlier dye based inks.
As the inkjet industry investigates new printhead designs, the tendency is toward using permanent or semi-permanent printheads in what is known in the industry as an xe2x80x9coff-axisxe2x80x9d printer. In an off-axis system, the printheads carry only a small ink supply across the printzone, with this supply being replenished through tubing that delivers ink from an xe2x80x9coff-axisxe2x80x9d stationary reservoir placed at a remote stationary location within the printer. There are a variety of advantages associated with these off-axis printing systems, but the permanent or semi-permanent nature of the printheads requires special considerations for servicing, particularly when wiping ink residue from the printheads, which must be done without any appreciable wear that could decrease printhead life. To accomplish this objective, an ink solvent has been used in an off-axis printer, specifically the DeskJet(copyright) 2000C Professional Series color inkjet printer, sold by the present assignee Hewlett-Packard Company. In this ink solvent system, a polyethylene glycol (xe2x80x9cPEGxe2x80x9d) compound is stored in a porous medium such as a plastic or foam block that is in intimate contact with a reservoir, with this porous block having an applicator portion exposed so the elastomeric wiper can contact the applicator. This elastomeric wiper moves across the applicator to collect PEG, which is then wiped across the printhead to dissolve accumulated ink residue and to deposit a non-stick coating of PEG on the printhead face to retard farther collection of ink residue. The PEG fluid also acts as a lubricant, so the rubbing action of the wiper does not unnecessarily wear the printhead. Other wiper systems without a solvent have also been sold by the Hewlett-Packard Company in the DeskJet(copyright) 850C, 855C, 870C and 890C models of color inkjet printers. These scraper systems used a rotary tumbler to wipe the printheads. Another solventless wiper scraper system has been sold by the present assignee, the Hewlett-Packard Company, in the DeskJet(copyright) 720C, 722C, 710C, 712C, 810C, 812C, 830C, 832C, 880C, 882C, 895C and 970C models of inkjet printers, which used a translating pallet to wipe the wipers across the printheads.
All of the Hewlett-Packard Company""s DeskJet(copyright) printer models mentioned in the paragraph above used wiper assemblies having the cross sectional configuration shown in FIGS. 4-6 of the drawings. FIG. 4 is a side view of a wiper assembly W at rest. FIGS. 5 and 6 show side views of the wiper assembly W making a two-pass wiping stroke, first to the right in FIG. 5, then to the left in FIG. 6, removing ink residue R from an external surface of an orifice plate of printhead P. The wiper assembly W has a first elastomeric wiper blade W1 and a second wiper blade W2 which are mounted to a sled S which moves the blades past the stationary printhead P to wiper the ink residue, Q and other debris from the orifice plate. This earlier dual-blade wiper system is described at length in U.S. Pat. No. 5,614,930, currently assigned to the Hewlett-Packard Company, and was first used in the Hewlett-Packard Company""s DeskJet(copyright) 850C color inkjet printer. The
DeskJet(copyright) model 850C printer employed a revolutionary rotary, orthogonal wiping scheme where the wipers ran along the length of the linear arrays, wicking ink I from one nozzle to the next. This wicked ink I acted as a solvent to break down ink residue accumulated on the nozzle plate. To facilitate this wicking action and subsequent printhead cleaning accomplish this wiping action, the wiper blades W1 and W2 have special contours at their tips. The blades W1 and W2 are mirror-images of each other, having outboard rounded edges R1 and R2, respectively, and inboard angular wiping edges A1 and A2, respectively. The rounded edges encounter the nozzles first and form a capillary channel between the blade and the orifice plate to wick liquid ink I from the nozzles as the wipers moved orthogonally along the length of the nozzle arrays, as shown for edge R2 in FIG. 5 and edge R1 in FIG. 6. The wicked ink I is pulled by the rounded edges R1, R2 of the leading wiper blade to the next nozzle in the array, where the ink I acts as a solvent to dissolve dried ink residue 9 accumulated on the printhead face plate. The angular edge of the trailing wiper blade then scraps the dissolved residue Qxe2x80x2 from the orifice plate, as shown for edge A1 in FIG. 5 and edge A2 in FIG. 6. The black ink wiper had notches cut in the tip which served as escape passageways for balled-up ink residue to be moved away from the nozzle arrays during the wiping stroke.
Unfortunately, the dual bladed wiping assembly W of FIGS. 4-6 required a back-and-forth slewing motion, first in the direction of arrow D1 (FIG. 5), then in the opposite direction of arrow D2, to wipe the ink residue and foreign debris. Q, Qxe2x80x2 from the printhead P. The back-and-forth wiping strokes were required to mask any defects in the wiper tip. Since the wiper tips are non-uniform, the redundancy in using two different surfaces for wiping masks the tip imperfections because there is an extremely low likelihood that both blades will have the same imperfections at the same lateral location across their tips. Thus, on each pass, a different wiping edge is used to clean the printhead, specifically, edges R2 and A1 when traveling in the D1 direction in FIG. 5, and edges R1 and A2 when traveling in the D2 direction in FIG. 6. The problem with this bi-directional wiping scheme is that it severely reduced the printer""s throughput, a printer rating measured in pages per minute, because of the time required to slew the wiper back-and-forth to complete a wiping routine. Especially as the length of printhead nozzle arrays increases, nearing one inch (2.54 centimeters), wiping cycles of over three seconds are anticipated when using this earlier bi-directional wiping scheme. Given the fact that it is desirable to wipe the printhead not only before a printjob, but also periodically during a printjob, this bi-directional operation began to seriously impact desired throughput goals.
Thus, a need exists for an inkjet printhead cleaning system which wipes ink residue and ink solvent from the printhead more quickly without impacting the throughput rating of a unit.
According to one aspect of the present invention, a single-pass wiping system is provided for cleaning ink residue from an inkjet printhead in an inkjet printing mechanism. The wiper system includes a platform moveable through a wiping stroke, along with a first wiper blade and a second wiper blade each supported by the platform. A third wiper blade is supported by the platform between the first wiper blade and the second wiper blade to wipe ink residue from the printhead during a unidirectional wiping stroke through contact first with the first wiper blade, followed by contact with the third wiper blade, followed by contact with the second wiper blade.
According to another aspect of the present invention, an inkjet printing mechanism is provided with a single-pass wiping system as described above.
According to yet another aspect of the present invention, a method is provided for cleaning ink residue from an inkjet printhead in an inkjet printing mechanism, including the step of providing a first wiper blade, a second wiper blade, and a third wiper blade, each supported by the platform, with the third wiper blade located between the first wiper blade and the second wiper blade. In a wiping step, ink residue is wiped from the printhead in a unidirectional wiping stroke by first wiping the printhead with the first wiper blade, followed by wiping the printhead with the third wiper blade, followed by wiping the printhead with the second wiper blade.
An overall goal of the present invention is to provide an inkjet printing mechanism which prints sharp vivid images over the life of the printhead and the printing mechanism, particularly when using fast drying pigment or dye-based inks, whether dispensed from an off-axis system or from a replaceable ink cartridge system.
Another important goal of the present invention is to provide a single-pass wiper system and method for wiping an inkjet printhead in an inkjet printing mechanism, without seriously impacting the throughput of a unit to provide consumers with a fast inkjet printing mechanism.
Still another goal of the present invention is to provide a single-pass wiper system for cleaning printhead wipers in an inkjet printing mechanism which is quieter than earlier systems, and which thus provides consumers with a reliable, quiet inkjet printing unit.